The present invention relates to a method for fabricating a semiconductor device; and, more particularly, to a method for forming a contact plug with a silicon thin film in a semiconductor device.
Recently, the size of a contact plug decreases as a level of integration of a semiconductor device progressively advances. Due to this decreased size of the contact plug, contact resistance of a typically used silicon plug conversely increases. Especially, an oxide formed at an interface of the contact plug is one of causes for increasing the contact resistance of the silicon plug with multi-crystals. Hence, a cleaning process is applied to remove the oxide in order to reduce the contact resistance of the silicon plug with multi-crystals.
However, in case of removing an oxide layer by cleaning a semiconductive substrate through an ex-situ cleaning process, a native oxide layer is formed while the semiconductive substrate completed with the ex-situ cleaning process is loaded to deposition equipment. For this reason, it is impossible to remove completely the oxide layer formed at the interface of the contact plug. Therefore, if the size of the contact plug decreases with a state that the native oxide layer still exists, the contact resistance increases in more extents. Accordingly, an in-situ cleaning process should be used in order to maximally suppress the generation of the native oxide layer.
A conventional polysilicon plug process is mostly carried out in a tube-type deposition equipment or a single wafer-type deposition equipment.
In case of forming the contact plug by depositing a silicon thin film through the tube-type deposition equipment, it is possible for the silicon thin film to obtain a good step coverage property but impossible to perform the in-situ cleaning process. Hence, the silicon thin film is inevitably deposited after performing the ex-situ cleaning process. However, the native oxide layer is formed at a procedure of loading a wafer to the tube-type deposition equipment for depositing the silicon thin film.
Since the singe wafer-type deposition equipment have a cleaning function, it is possible to perform the in-situ cleaning process and deposit the silicon thin film under this in-situ environment, thereby preventing the native oxide layer from being generated.
As mentioned the above, if the contact plug is formed in the single wafer-type deposition equipment, it is possible to remove the native oxide layer formed at the interface of the contact plug by applying a bake or a rapid thermal process (RTP) in an atmosphere of hydrogen or a cleaning process. However, compared to use of the tube-type deposition equipment, such characteristics as uniformity and step coverage become poor when the contact plug size is smaller. In particular, a level of uniformity in the contact resistance decreases.
Also, because of the reduced contact size and increase of an aspect ratio, a sufficient gap-fill should be proceeded by depositing the silicon. However, the single wafer-type deposition equipment has poor gap-fill ability, compared to the tube-type deposition equipment.
In case of forming a contact hole by etching a typical BPSG layer, a cleaning process with a hydrogen-rapid annealing is suggested for removing the native oxide layer. However, when the cleaning process with the hydrogen-rapid annealing is proceeded in a state of the exposed BPSG, it is unable to prevent degradations of device properties and the decrease of the contact resistance due to externally diffused boron.
FIG. 1 is a diagram evaluating concentrations of phosphorus diffused from a boro-phospho-silicate glass (BPSG) layer.
Referring to FIG. 1, a barrier layer is formed on a surface of the BPSG layer through a dry cleaning process (shortly abbreviated as Dry CLN in FIG. 1) or a hydrogen-thermal annealing process (shortly abbreviated as H2-anneal in FIG. 1). This formation of the barrier layer means that extensive external diffusions of boron occur during an initial stage of the process.
Since the BPSG layer from which boron is externally diffused can be hardened, the typical hydrogen-annealing process including the hydrogen-rapid thermal process is unable to prevent the external diffusions of boron from the BPSG layer during an initial stage of the process.
It is, therefore, an object of the present invention to provide a method for forming a contact plug in a semiconductor device capable of preventing a decrease of contact resistance and degradation of device properties due to external diffusions of boron within an inter-layer insulating layer.
In accordance with an aspect of the present invention, there is provided a method for forming a contact plug in a semiconductor device, comprising the steps of: forming a contact hole by etching an insulating layer on a substrate; cleaning the contact hole by employing a hydrogen-rapid thermal process (H2-RTP) with flowing a gas containing phosphorus; and filling the contact hole with a silicon layer.
In particular, the step of cleaning the contact hole by employing the H2-RTP is proceeded by cooling a temperature that has been rise instantaneously up to a range between about 900xc2x0 C. and 950xc2x0 C. with a heating rate ranging from about 10xc2x0 C. per second to about 100xc2x0 C. per second in an atmosphere of H2. Also, the gas containing phosphorus includes a PH3 gas diluted in H2 gas with a ratio of about 1% to 10%. Furthermore, the PH3 gas is flowed with a quantity ranging from about 30 sccm to about 500 sccm up to a temperature ranging between about 900xc2x0 C. and about 950xc2x0 C.
In accordance with another aspect of the present invention, there is provided a method forming a contact plug in a semiconductor device, comprising the steps of: forming a contact hole by etching an insulating layer on a substrate; cleaning the contact hole with a hydrogen-rapid thermal process (H2-RTP) and simultaneously flowing HCl gas from a peak temperature of the H2-RTP; and forming a silicon thin layer on the substrate until filling the cleaned contact hole.
The HCl gas is flowed with a quantity ranging from about 50 sccm to about 500 sccm.